University of Maine

About: University of Maine is a education organization based out in Orono, Maine, United States. It is known for research contribution in the topics: Population & Ice sheet. The organization has 8637 authors who have published 16932 publications receiving 590124 citations. The organization is also known as: University of Maine at Orono.

Generality of fractal 1/f scaling in catchment tracer time series, and its implications for catchment travel time distributions

Abstract: Catchment travel time distributions reflect how precipitation from different storms is stored and mixed as it is transported to the stream. Catchment travel time distributions can be described by the mean travel time and the shape of the distribution around the mean. Whereas mean travel times have been quantified in a range of catchment studies, only rarely has the shape of the distribution been estimated. The shape of the distribution affects both the short-term and long-term catchment response to a pulse input of a soluble contaminant. Travel time distributions are usually estimated from conservative tracer concentrations in precipitation and streamflow, which are analyzed using time-domain convolution or spectral methods. Of these two approaches,spectral methods are better suited to determining the shape of the distribution. Previous spectral analyses of both rainfall and streamflow tracer time series from several catchments in Wales showed that rainfall chemistry spectra resemble white noise, whereas the stream tracer spectra in these same catchments exhibit fractal 1/f scaling over three orders of magnitude. Here we test the generality of the observed fractal scaling of streamflow chemistry, using spectral analysis of long-term tracer time series from 22 catchments in North America and Europe. We demonstrate that 1/f fractal scaling of stream chemistry is a common feature of these catchments. These observations imply that catchments typically exhibit an approximate power-law distribution of travel times, and thus retain a long memory of past inputs. The observed fractal scaling places strong constraints on possible models of catchment behavior, because it is inconsistent with the exponential travel time distributions that are predicted by simple mixing models.

Resolver signal requirements for high accuracy resolver-to-digital conversion

Abstract: Tracking resolver-to-digital (R/D) conversion has emerged as the most robust method for obtaining high-resolution position information from resolvers. When driven by ideal resolver signals, tracking R/D converters currently offer position resolutions up to 2/sup 16/ quantization intervals/period (16-b resolution), and accuracies to 2/sup 14/ intervals/period (14-b accuracy). The effects of nonideal resolver signal characteristics commonly encountered in practice are investigated. Expressions for the position error reported by an R/D converter due to amplitude imbalance, quadrature error, inductive harmonics, reference phase shift, excitation signal distortion, and disturbance signals are found. From these expressions, bounds on the position accuracy achievable in practical resolver-based position-sensing systems are determined. >

Gendered cybersupport: a thematic analysis of two online cancer support groups.

Abstract: Within the last few years numerous support groups have emerged on the Internet, presenting new opportunities for patients to communicate with health care professionals and other patients. The present study examines discourse within online cancer support groups, increasing our understanding of sex differences in cybersupport. Two reproductive cancer groups were chosen for this investigation, the Ovarian Problems Mailing List (OPML) and the Prostate Problems Mailing List (PPML), making sex of the patient recognizable. Phenomenological thematic analysis was employed to describe and interpret messages sent and received. Analyses for the two groups were compared. Generally, it was found that the two online listservs provided opportunities for cancer patients to receive support, within western society's accepted forms of gendered communication.

Experimental inducement of nitrogen saturation at the watershed scale

Abstract: In some streams and lakes of the mid-Appalachian, New York, and Pennsylvania regions of the United States, NO; concentrations are now elevated for much of the year (12,13). In southern Norway, lake surveys conducted 10 years apart demonstrated widespread increases in NO3-, presumably due to continued atmospheric loading of ni- trogen

Canopy processing of acidic precipitation by coniferous and hardwood forests in New England.

Abstract: There are several important factors that may influence how forest canopies interact with acidic deposition, including forest community species composition, phenological status, and differences in atmospheric loading of strong acids. Results from comparative throughfall chemistry studies in New Hampshire, where precipitation pH is 4.1, indicate that northern hardwood canopies produce a throughfall solution chemistry that is less acid and higher in basic cations than either direct precipitation or throughfall solutions derived from nearby subalpine balsam fir forests. Neutralization of acid precipitation in the hardwood canopy appears to occur through two major processes: ion exchange removal of free H+ by the foliage, and Bronsted base leaching from the plant canopy. Data obtained during the period of senescence preceding leaf-drop suggest a strong link between alkalinity release and potassium leaching in the hardwood canopy. Compared with the hardwood canopy, the coniferous forest canopy exhibits several distinct quantitative differences in canopy processing.